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, 279 (1743), 3827-33

Ground Squirrel Tail-Flag Displays Alter Both Predatory Strike and Ambush Site Selection Behaviours of Rattlesnakes

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Ground Squirrel Tail-Flag Displays Alter Both Predatory Strike and Ambush Site Selection Behaviours of Rattlesnakes

Matthew A Barbour et al. Proc Biol Sci.

Abstract

Many species approach, inspect and signal towards their predators. These behaviours are often interpreted as predator-deterrent signals--honest signals that indicate to a predator that continued hunting is likely to be futile. However, many of these putative predator-deterrent signals are given when no predator is present, and it remains unclear if and why such signals deter predators. We examined the effects of one such signal, the tail-flag display of California ground squirrels, which is frequently given both during and outside direct encounters with northern Pacific rattlesnakes. We video-recorded and quantified the ambush foraging responses of rattlesnakes to tail-flagging displays from ground squirrels. We found that tail-flagging deterred snakes from striking squirrels, most likely by advertising squirrel vigilance (i.e. readiness to dodge a snake strike). We also found that tail-flagging by adult squirrels increased the likelihood that snakes would leave their ambush site, apparently by elevating the vigilance of nearby squirrels which reduces the profitability of the ambush site. Our results provide some of the first empirical evidence of the mechanisms by which a prey display, although frequently given in the absence of a predator, may still deter predators during encounters.

Figures

Figure 1.
Figure 1.
Rattlesnake responses (strike, 1; no strike, 0) to squirrels that either tail-flagged (black triangle) or not (grey diamond) at various distances within their observed strike range (31 cm). All data points were either 1 or 0; we jittered the location of data points around 1 and 0 to avoid overlapping values. The black solid line indicates our model's predicted probability of snakes striking at tail-flagging squirrels as a function of distance. The grey-dashed line indicates the predicted probability of snakes striking at non-tail-flagging squirrels as a function of distance.
Figure 2.
Figure 2.
Frequency of tail-flagging and non-tail-flagging ground squirrels that attempted to dodge rattlesnake strikes. Black bars, no dodge; grey bars, dodge.
Figure 3.
Figure 3.
Plot of the estimated likelihood (hazard ratio ± 95% confidence intervals) of rattlesnakes (a) abandoning an ambush site and (b) striking a squirrel within an ambush site, after each tail-flagging display from an adult, pup or both. The dashed line with y-intercept = 1 indicates the likelihood under the null hypothesis.

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